Method of Assembling Constant Velocity Joint of Tripod Type

ABSTRACT

A method of assembling a constant velocity joint comprises: measuring a maximum non-interfering thickness of a trunnion that can be inserted into an inner roller without interference while inclining the inner roller by a predetermined degree; providing the trunnion to have a cross sectional shape, taken in a direction perpendicular to the trunnion, with a first thickness at one lateral side and a second thickness at the other lateral side, where one or both of the first and second thicknesses have a size the same as or 0-30% smaller than the maximum non-interfering thickness of the trunnion; inclining the inner roller to assume the predetermined degree of inclination; positioning the inclined inner roller onto the trunnion and completely assembling thereto without excessive external force.

REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.11/947,307 filed on Nov. 29, 2007, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a constant velocity joint of tripodtype, which is disposed between a drive shaft and a driven shaft coupledto each other and typically used in a drive axle of, for example, anautomobile for transmitting rotational torque between the rotatingshafts.

BACKGROUND OF THE INVENTION

Tripod type constant velocity joints are well known in the automobileindustry as one type of constant velocity joints used in the drivesystem of automobiles to transfer a uniform torque and a constant speed,while operating with a wide range of joint angle. For instance, oneexample of the tripod type constant velocity joint was illustrated inJapanese Patent Application, S62-233522 as shown in FIGS. 1-2. Thistripod type constant velocity joint typically includes tripod 15 fixedto an end of the second rotating shaft, which functions as a drivenmember, and hollow cylindrical housing 13 fixed to an end of the firstrotating shaft 12 which functions as a drive member. Grooves 16 areformed at three locations on the inner face of the housing 13 at equalspacing in the circumferential direction and extend in the shaftdirection of the housing 13.

The tripod 15 comprises a boss 17 connected to the second rotating shaft14, and trunnions 18 each having a cylindrical shape and extendingradially from three locations at equal spacing around the boss 17. Eachtrunnion18 has a roller 19 fixed at a distal end of the trunnion andwith needle rollers 20 engaged therein. In this arrangement, each roller19 can freely rotate about the trunnion 18 while also be displaced inthe axial direction of the trunnion 18. The constant velocity movementbetween the first and second rotating shafts is ensured with the rollers19 rotatably and displaceably engaging in the grooves 16 disposed alongthe inner face of the housing 13. In order to facilitate the slidingmovement, a pair of side faces 16 a are formed in circular recesses oneach side of the respective grooves 16, and each roller 19 is supportedrotatably and pivotally along the side faces 16 a of the grooves.

As the first rotating shaft 12 rotates, its rotational force istransmitted from housing 13, through roller 19, needle rollers 20,trunnions 18, and to the boss 17 of the tripod 15. This makes the boss17 rotate, and which also causes rotation of the second rotating shaft14. When the joint angle of the two rotating shafts 12 and 14 is notzero, a central axis of the first rotating shaft 12 is not aligned withthat of the second rotating shaft 14, and each of the trunnion 18displaces relative to the side face 16 a of the guide grooves 16 to movearound the tripod 15, as shown in FIG.1 and FIG. 2. As a result, therollers 19 supported at the ends of the trunnions 18 move along theaxial directions of the trunnions 18, respectively, while rolling on theside faces 16 a of the guide grooves 16. Such movement ensures that aconstant velocity between the first and second rotating shaft isachieved.

When the first and second shafts rotate with a joint angle present, eachroller 19 moves with complexity. For example, each roller 19 moves inthe axial direction of the housing 13 along each of the side faces 16 aof the respective guide grooves 16, while the rollers 19 change inorientation and further displace in the axial direction of the trunnion18. Such movement of the rollers 19 cannot cause a relative movementbetween a peripheral outside face of each of the rollers 19 and each ofthe side faces 16 a to be smoothly made. Thus, a relatively largefriction occurs between the faces. As a result, this tripod typeconstant velocity joint produces three-directional axial forces as theshafts rotate. In the application of a tripod joint to the vehicles, itis known that the axial forces may cause a transverse vibrationtypically referred to as “shudder”, if a large torque is transmittedwith a relatively large joint angle present.

In order to restrain or reduce such conventional shudder problems,various suggestions have been introduced in the art. For example, U.S.Pat. No. 6,533,668 B2 discloses a constant velocity joint constructionwhich can reduce the shudder problem by modifying the conventionalcontact ellipse. As shown in FIG. 3( a), the trunnion 18′ of this jointis produced to have an elliptical cross-section when viewed from an axisnormal to the trunnion shaft. As a result, the elliptical sectionincludes a shorter diameter “B” in the length not receiving a load, anda longer diameter “A” in the length for receiving a load. This is tomake a contact pattern between the inner spherical surface of the innerroller 19 b and the trunnion 18′ relatively closer to a circle, whenreceiving a torque for a load. As a result, a longer contact diameter a′(FIG. 3( b)) becomes smaller than the longer contact diameter ofpreviously known constant velocity joints which have trunnions with acircular cross-section, for example, such as the trunnions shown inFR275280 and Japanese Publication No. H3-172619. However, it still hasan elliptical contact pattern even though the degree of ellipse isreduced because a curvature of a longitudinal cross-section of thetrunnion 18′ formed by radius r2 and R is not equal to a curvature of anaxial cross-section of the trunnion 18 formed by an ellipse 18 a definedas a longer diameter A and a shorter diameter B.

When these joints rotate with a joint angle present upon receivingloads, a pivotal movement of counterclockwise direction of trunnion 18′causes a pivotal sliding action to take place on the contact ellipse.Then the pivotal sliding action operates as a frictional spinning momentso as to change a rolling direction of the roller assembly 19, whichcomprises the inner roller 19 b and the outer roller 19 a with needlebearings 20 engaged there-between. As a result, direction of the rollerassembly 19 changes and it becomes in contact with inner or outer faceof the guide groove 16, and thus, increasing a frictional contact forcethere-between. Moreover, the roller assembly 19 displaces not toparallel to the guide groove 16. Hence it is difficult for the rollerassembly 19 to be smoothly rolled, and causes a significant rollingresistance.

Moreover, for manufacturing the constant velocity joint of FIG. 3, thereare considerable difficulties not only to machine a complex sphericalsurface defined by a curvature of a longitudinal cross-section of thetrunnion 18′ formed by radius r2 and R and the ellipse shape 18′ definedas a longer diameter A and a shorter diameter B, but also to measure thetrunnion 18′ having a complex three dimensional profile, in terms ofboth inspection and quality control. These difficulties cause thecontact pattern mentioned above to be inconsistent in terms of quality,which leads to high costs in manufacturing perspective and also topotential quality control issues.

Moreover, in order to provide grease-entry space for better durabilityand smooth operation, space “s” is provided between the upper and lowerends at the inner face of the inner roller 19 b and the upper and lowerportions of the spherical face of the trunnion 18′, as shown in FIG. 3(a). However, due to the relative pivotal movement of the trunnion 18′within the open inner surface of the inner roller 19 b, the grease flowsout easily from the open space “s” and sufficient amount of greasecannot be retained in the open space “s” disposed between the sphericalface of the trunnion 18′ and the upper and lower ends at the inner faceof the inner roller 19 b. As a result, the joint cannot be lubricatedeffectively and often suffers aggravated friction problems. This becomesmore problematic when the grease is in high density condition, forexample, during the initial driving stage of automobile particularly ata cold outside temperature, which causes a significant rollingresistance in the drive system.

SUMMARY OF THE INVENTION

In order to solve the above described and other problems or drawbacksknown in the prior art constant velocity joints, the applicant (namely,the inventor) of this invention suggested several improved constantvelocity joints and assembly methods thereof, for example, such asdisclosed in application Ser. No. 11/840,194 filed Aug. 16, 2007 andentitled “CONSTANT VELOCITY JOINT OF TRIPOD TYPE”, which is now issuedas U.S. Pat. No. 7,878,914, which is a continuation-in-part of U.S.patent application Ser. No. 11/750,138 filed on May 17, 2007, which isnow issued as U.S. Pat. No. 7,819,752, the entire contents of which areincorporated herein by reference. The present invention provides furthermodifications and/or improvements to the applicant's prior applicationsSer. No. 11/750,138 and Ser. No. 11/840,194.

According to certain preferred embodiments, the constant velocity jointsdisclosed in the applicant's pending applications Ser. No. 11/750,138and Ser. No. 11/840,194 include, among other members, plural (e.g.,three) trunnions each having a pair of cylindrical protrusions protrudeda predetermined distance from the outer surface of the trunnion in adirection generally perpendicular to the axis of the correspondingtrunnion, as illustrated in FIG. 4. These cylindrical protrusionsprovide a reduced contact surface between the trunnion and the innerface of the corresponding inner roller, and thus, reducing thefrictional spinning force acting on the contact ellipse made between theouter face of the trunnion and the inner face of the inner roller, dueto the pivotal sliding movement of the trunnion axis known in the art.

The constant velocity joints disclosed in the applicant's previousapplications further provide a sufficient lubrication mechanism betweenthe inner race and the trunnion (in particular, between the protrudedcylindrical protrusions and the inner surface of the inner race), andbetween the outer roller, the needle rollers, and the inner roller, tominimize the rolling resistance when rotating with any joint anglepresent. Moreover, methods of assembling the joints are also provided,in which the joint is also configured to prevent from an accidentaldisassembly in normal operating condition.

Accordingly, one object of the present invention is to provide a tripodtype constant velocity joint which is further modified and/or improvedfrom those disclosed by the above-identified inventions of theapplicant.

Another object of the present invention is to provide a tripod typeconstant velocity joint having a durable structure and mechanicalstrength and also reliable under adverse and severe operatingconditions.

Another object of the present invention is to provide a tripod typeconstant velocity joint which has a reliable structure and easy toassemble. Another object of the present invention is to provide areliable tripod type constant velocity joint and methods of assemblingthe joint, in which the joint is also configured not to be accidentallydisassembled in operation. Further objects and features of the presentinvention can be recognized from the accompanied drawings and thefollowing descriptions of the invention. A further object of the presentinvention is to provide a tripod type constant velocity joint having asufficient lubrication mechanism, for example, between the inner raceand the trunnions, and between the outer roller, the needle rollers, andthe inner roller, to minimize the rolling resistance when rotating withany joint angle present.

The constant velocity joint of the present invention includes, amongother members, plural (e.g., three) trunnions each having two opposingspherical contact surfaces disposed in the directions subject to theload and also having two opposing and generally planar or partiallycurved or angled surfaces disposed in the directions perpendicular tothe spherical surfaces and not subjecting to the load, for example, asillustrated in FIGS. 5, 6, 10, 15-17 to be described later in details.According to one preferred embodiment, the trunnions include a groove ofcircular or oval shape provided at the central location of eachspherical contact surface of the trunnions, and thereby, define a mainspherical contact area in circular or oval shape of predetermined sizeat each of the spherical surface of the trunnions, for example, asillustrated in FIGS. 5, 6, and 9-11 to be described later in details.According to one preferred embodiment, the lateral spherical surfaceoutside of the central main contact area has the same spherical radiusof contact as that of the central main spherical contact surface andprovides an additional contact surface, and thereby, enhancing themechanical strength and durability of the trunnions which can endure apotential high stress concentration on the contact surface.Alternatively, owing to the additional lateral contact surface, theoverall size of each trunnion can be reduced (particularly, whencompared to the embodiment of FIG. 4) while satisfying the mechanicalstrength requirements of the trunnions. This may also provide apotential to reduce the entire size of the tripod and the constantvelocity joint.

The circular groove recessed from the spherical contact surface of thetrunnion is for retaining additional grease therein to further lubricatethe contact surface between the trunnions and the generally sphericalinner surface of the inner race, thus, further enhancing the durabilityand life time of the joints. This lubrication is in addition to the mainlubrication to be done by the grease retained in the space between theinner surface of the inner race and the two opposing and generallyplanar or partially curved or angled surfaces disposed in the directionsperpendicular to the generally spherical surfaces and not subjecting tothe load.

In an alternative embodiment, the circular or oval groove can be omittedfrom the trunnions, for example, as illustrated in FIGS. 7 and 8 and tobe described later in details. In this embodiment, the contact surfacebetween the spherical contact surface of trunnions and the generallyspherical inner surface of the inner race is lubricated by the greaseretained only in the space between the spherical inner surface of theinner race and the two opposing and generally planar or partially curvedor angled surfaces disposed in the directions perpendicular to thespherical contact surfaces, that are not subject to the load.

According to another preferred embodiment of the present invention, thetrunnions of the constant velocity joint include two opposing sphericalcontact surfaces disposed in the directions subject to the load, and twoopposing and generally planar or partially curved or angled surfacesdisposed in the directions perpendicular to the spherical contactsurfaces, that are not subject to the load. According to one preferredembodiment, with the two opposing and generally planar or partiallycurved or angled surfaces disposed in the directions perpendicular tothe spherical surfaces, the trunnion has a complex shape with its crosssection, taken in a direction perpendicular to the trunnion shaft,having a thickness gradually varying between a larger thickness T and asmaller thickness S relative to the axial distance in cross section fromthe neck of the trunnion, while enhancing the mechanical strength anddurability of the trunnion and also enabling an easy assembly with theinner roller.

In one embodiment, the cross-sectional shape taken at the upper portionof the trunnion has a larger thickness “T” at the left side and isgradually decreased until it reaches a smaller thickness “S” at theright side of the trunnion; the cross-sectional shape taken at the lowerportion of the trunnion has a smaller thickness “S” at the left side andis gradually increased until it reaches a larger thickness “T” at theright side of the trunnion; and the cross-sectional shapes in-betweenthe upper and lower portions are gradually varied from thecross-sectional shape at the upper portion to the cross-sectional shapeat the lower portion of the trunnion, for example, as illustrated inFIGS. 10( a)-10(f) to be described later in details.

In another embodiment, the cross-sectional shape taken at the upperportion of the trunnion has the larger thickness “T” at the left sideand the smaller thickness “S” at the right side of the trunnion, and thecross-sectional contour between the left and right sides is graduallyvaried to define a convex shape as a whole, preferably with the contourthereof defined by a surface radius R, as illustrated in FIG. 15( b). Tothe contrary, the cross-sectional shape taken at the lower portion ofthe trunnion has the smaller thickness “S” at the left side and thelarger thickness “T” at the right side, and the cross-sectional contourbetween the left and right sides is gradually varied to define a convexshape as a whole, preferably with the contour thereof defined by asurface radius R, as illustrated in FIG. 15( c). The cross-sectionalshapes in-between the upper and lower portions are gradually varied fromthe cross-sectional shape at the upper portion to the cross-sectionalshape at the lower portion of the trunnion. As a result, thecross-sectional shape taken at the middle portion of the trunnionincludes a generally planar shape or a slightly convex shape.

According to one preferred embodiment of the present invention, in orderto solve the above described problems and other problems to berecognized by following disclosure, a constant velocity joint for adrive system with a first rotating shaft and a second rotating shaftcoupled with the constant velocity joint, comprises:

a hollow housing having a plurality of guide grooves therein, the guidegrooves extending in an axial direction of the housing and spacedequally apart in a circumferential direction of the housing;

a tripod having a plurality of trunnions, each trunnion positioned in acorresponding one of the guide grooves of the hollow housing; and

a roller assembly including an inner roller, the inner roller having aspherical inner face for receiving a corresponding one of the trunnionstherein, and an outer roller mounted on an outer face of each innerroller, the roller assembly for transmitting a load between the firstand second rotating shafts to drive the driving system;

wherein each trunnion includes two opposing spherical contact surfacesdisposed in the directions subject to the load, and two opposing sidesurfaces disposed between the two opposing spherical contact surfacesand in the directions perpendicular to the spherical surfaces and notsubjecting to the load;

wherein a cross sectional shape of the trunnion, the cross section takenin a direction perpendicular to the longitudinal axis of the trunnion,has a thickness at one or both lateral sides of the trunnion the same asor slightly less than a maximum non-interfering thickness of thetrunnion, the maximum non-interfering thickness measured with the innerroller inclined by a predetermined degree relative to the longitudinalaxis of the trunnion to assemble the trunnion into the inner roller.

According to another preferred embodiment of the present invention, aconstant velocity joint for a drive system having a first rotating shaftand a second rotating shaft coupled with the constant velocity joint,comprises:

a hollow housing having a plurality of guide grooves therein, the guidegrooves extending in an axial direction of the housing and spacedequally apart in a circumferential direction of the housing;

a tripod having a plurality of trunnions, each trunnion positioned in acorresponding one of the guide grooves of the hollow housing; and

a roller assembly including an inner roller, the inner roller having aspherical inner face for receiving a corresponding one of the trunnionstherein, and an outer roller mounted on an outer face of each innerroller, the roller assembly for transmitting a load between the firstand second rotating shafts to drive the driving system;

wherein each trunnion includes two opposing spherical contact surfacesdisposed in the directions subject to the load, and two opposing sidesurfaces disposed between the two opposing spherical contact surfacesand in the directions perpendicular to the spherical surfaces and notsubjecting to the load;

wherein a cross sectional shape of the trunnion, the cross section takenin a direction perpendicular to the longitudinal axis of the trunnion,has a thickness at one or both lateral sides of the trunnion the same asor smaller than a maximum non-interfering thickness of the trunnion, themaximum non-interfering thickness measured with the inner rollerinclined by a predetermined degree relative to the longitudinal axis ofthe trunnion to assemble the trunnion into the inner roller;

wherein a groove of circular or oval shape is formed on each of the twoopposing spherical contact surfaces, the groove for retaining greasetherein to lubricate contact surfaces between the inner roller and thetrunnion.

According to another preferred embodiment of the present invention, amethod of assembling a trunnion of a constant velocity joint into aninner roller of a roller assembly, comprises the steps of:

providing a roller assembly for a constant velocity joint, the rollerassembly including an outer roller, and an inner roller having aspherical inner face;

providing a constant velocity joint having a tripod with a pluralitytrunnions, each trunnion including two opposing spherical contactsurfaces disposed in the directions subject to the load, and twoopposing side surfaces disposed between the two opposing sphericalcontact surfaces and in the directions not subject to the load;

measuring a maximum non-interfering thickness of the trunnion which is amaximum thickness of the trunnion, having the two opposing sphericalcontact surfaces of a diameter, that can be inserted into the innerroller without interference while inclining the inner roller by apredetermined degree relative to the longitudinal axis of the trunnion;

providing the trunnion to have a cross sectional shape, the crosssection taken in a direction perpendicular to the longitudinal axis ofthe trunnion, with a thickness at one or both lateral sides of thetrunnion the same as or 0-30% smaller than the maximum non-interferingthickness of the trunnion;

inclining the inner roller with respect to the trunnion to assume thepredetermined degree of inclination;

positioning the inclined inner roller partially onto the trunnion, byplacing a lower right inner face of the inner roller on an upper rightside of the trunnion and positioning a lower left face of the innerroller to meet a lower left side of the trunnion; and

completely positioning the inner roller by pushing or rotating a rightupper side of the inclined inner roller down without applying excessiveexternal force.

The trunnion preferably includes a neck portion below the trunnion. Inone embodiment, the center line of neck portion generally coaxial withthe longitudinal axis of the trunnion. In another embodiment, the centerof the neck portion is offset a distance from the longitudinal axis ofthe trunnion to facilitate assembly of the trunnion into the innerroller.

According to one preferred embodiment, the trunnion is provided to havea cross sectional shape, throughout the entire cross sections taken inthe direction perpendicular to the longitudinal axis of the trunnion,with the first thickness at the one lateral side being larger than thesecond thickness at the other lateral side, and the first and secondthicknesses are defined by the equations of:

0.5 D≦S≦0.7 D;

1.0 S≦T≦1.2 S;

where S represents the second thickness at the other lateral side of thetrunnion which is the same as or smaller than the maximumnon-interfering thickness, T represents the first thickness at the onelateral side of the trunnion which is larger than the maximumnon-interfering thickness of the trunnion, and D represents a sphericaldiameter of the trunnion.

According to another preferred embodiment, the trunnion is provided tohave a cross sectional shape, taken in the direction perpendicular tothe longitudinal axis of the trunnion, with the first thickness at theone lateral side being larger than the second thickness at the otherlateral side, and the first and second thicknesses are defined by theequations of:

0.5 D≦S≦0.7 D;

1.0 S≦T≦1.2 S;

where S represents the second thickness at the other lateral side of thetrunnion which is the same as or smaller than the maximumnon-interfering thickness, T represents the first thickness at the onelateral side of the trunnion which is larger than the maximumnon-interfering thickness of the trunnion, and D represents a sphericaldiameter of the trunnion; and

wherein the cross sectional shape of the trunnion varies with thethickness gradually varying from the first lateral side of the trunnionto the second lateral side of the trunnion in an alternate mannerrelative to an axial distance from the center of the tripod, and in amanner such that, by said placing the lower right inner face of theinner roller on the upper right side of the trunnion and by saidpositioning the lower left inner face of the inner roller to meet thelower left side of the trunnion, the inclined inner roller is partiallypositioned onto the trunnion with its spherical inner face partiallyreceiving the upper right side of the trunnion with the thickness S andpartially receiving the lower left side of the trunnion with thethickness S.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described and other objects, features and advantages of thepresent invention will be more apparent from the presently preferredembodiments of the invention disclosed in the following description andillustrated in the accompanying drawings, in which:

FIG. 1 shows a perspective view of a conventional tripod type constantvelocity joint;

FIG.2 shows a side cross-sectional view of a conventional tripod typeconstant velocity joint;

FIGS. 3( a) and 3(b) show a partial cross-sectional view of a trunnionand a partial longitudinal cross-sectional view of the trunnion and theinner roller, according to a conventional tripod type constant velocityjoint;

FIG. 3( c) shows partial cross-sectional illustrating a frictionalspinning moment generated in the conventional tripod type constantvelocity joint of FIG. 3( a);

FIGS. 4( a) and 4(b) show a top view and a front view illustrating oneembodiment of the trunnion disclosed in applicant's prior applicationsSer. No. 11/840,194 and Ser. No. 11/750,138, which are now issued asU.S. Pat. No. 7,878,914 and U.S. Pat. No. 7,819,752, respectively;

FIG. 5( a) shows a front view of the trunnion according to one preferredembodiment of the present invention;

FIG. 5( b) shows a cross-sectional view of the trunnion, taken along thedirections A-A, B-B, and C-C in FIG. 5( a);

FIG. 5( c) shows a side view of the trunnion, seen from the directions Dand E in FIG. 5( a);

FIG. 6( a) shows a front view of the trunnion according to anotherpreferred embodiment of the present invention;

FIG. 6( b) shows a cross-sectional view of the trunnion, taken along thedirections A-A, B-B, and C-C in FIG. 6( a) and illustrating the twoopposing surfaces in the directions not subject to the load have acurved or convex contour;

FIG. 6( c) shows a side view of the trunnion, seen from the directions Dand E in FIG. 6( a);

FIG. 7( a) shows a front view of the trunnion according to anotherpreferred embodiment of the present invention, in which the trunniondoes not includes of the grooves of circular or oval shape shown in FIG.6( a);

FIG. 7( b) shows a cross-sectional view of the trunnion, taken along thedirections A-A, B-B, and C-C in FIG. 7( a);

FIG. 7( c) shows a side view of the trunnion, seen from the directions Dand E in FIG. 7( a);

FIG. 8( a) shows a front view of the trunnion according to anotherpreferred embodiment of the present invention, in which the trunniondoes not includes of the grooves of circular or oval shape shown in FIG.6( a);

FIG. 8( b) shows a cross-sectional view of the trunnion, taken along thedirections A-A, B-B, and C-C in FIG. 8( a) and illustrating the twoopposing surfaces in the directions not subject to the load have acurved or convex contour;

FIG. 8( c) shows a side view of the trunnion, seen from the directions Dand E in FIG. 8( a);

FIGS. 9( a) and 9(b) show a top view and a partial front side view ofthe trunnion according to another preferred embodiment of the presentinvention, in which the two opposing surfaces in the directionsperpendicular to the spherical surfaces have a cross-sectional shape,taken in a direction perpendicular to the trunnion shaft, which has awidth or thickness alternately varying between the lower and upperportions of the trunnion;

FIG. 10( a) shows a partial front view of the tripod having the trunnionof FIG. 9;

FIG. 10( b) is a top cross-sectional view of the trunnion taken alongthe line A-A in FIG. 10( a);

FIG. 10( c) is a top cross-sectional view of the trunnion taken alongthe line B-B in FIG. 10( a);

FIG. 10( d) is a top cross-sectional view of the trunnion taken alongthe line C-C in FIG. 10( a);

FIG. 10( e) is a right side view shown from the direction “D” in FIG.10( a);

FIG. 10( f) is a left side view shown from the direction “E” in FIG. 10(a);

FIG. 11 is a side prospective view illustrating the tripod of FIG. 10(a);

FIG. 12( a) is a partial side cross-sectional view illustrating aspatial relationship between the trunnion and the inner roller with theinner roller inclined by the angle a for assembly;

FIG. 12( b) a cross-sectional view of the trunnion taken along the lineC-C in FIG. 12( a);

FIG. 12( c) is a cross-sectional view of the trunnion taken along theline A-A in FIG. 12( a);

FIG. 13 shows a partial side cross-sectional view and a top viewillustrating a spatial relationship between the trunnion and the innerroller with the inner roller inclined by the angle a for assembly, inwhich the trunnion has a thickness “S” at the two lateral sides thereofnot interfering with the inner roller when assembling;

FIG. 14 shows a partial side cross-sectional view and a top viewillustrating a spatial relationship between the trunnion and the innerroller with the inner roller inclined by the angle a for assembly, inwhich the trunnion has a thickness “T” (larger than thickness “S”) atthe two lateral sides thereof which include the hatched areas “W”interfering with the inner roller when assembling;

FIG. 15( a) is a partial side cross-sectional view of the trunnionaccording to one preferred embodiment of the invention, thecross-sectional shape of the trunnion having a composite and varyingthickness between T and S in order to avoid the interference asillustrated in FIG. 14;

FIG. 15( b) is a cross-sectional view taken along A-A in FIG. 15( a);

FIG. 15( c) is a cross-sectional view taken along C-C in FIG. 15( a);

FIGS. 16( a) and 16(b) show partial side cross-sectional view and topview of the trunnion according to another preferred embodiment of theinvention, the cross-sectional shape of the trunnion having a thicknessvarying between T and S and side chamfered areas in order to avoid theinterference as illustrated in FIG. 14;

FIGS. 17( a) and 17(b) show partial side cross-sectional view and topview of the trunnion according to another preferred embodiment of theinvention, in which the center of trunnion neck is offset by a distanceΔ from the center of the tripod in order to avoid the assemblyinterference as illustrated in FIG. 14;

FIGS. 18( a)-18(d) illustrate another preferred embodiment of theinvention similar to the embodiment shown in FIG. 17; in which thecenter of trunnion neck is offset by a distance Δ from the center of thetripod, however with a cross-sectional shape of the trunnion differentfrom that of FIG. 17 as shown in FIGS. 18( a) and 18(b), and with theinner roller having two lower grooves of small size at one side of theinner roller as shown in FIG. 18( c) or one lower groove of bigger sizeat one side of the inner roller as shown in FIG. 18(d), provided inorder to avoid the assembly interference as illustrated in FIG. 14; and

FIG. 18( e) illustrates a method of assembling the joint of theinvention according to the embodiment shown in FIGS. 18( a)-18(d).

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 5-18 of the drawings, exemplary embodiments ofthe tripods of the tripod type constant velocity joints of the presentinvention and methods of assembling the joints are described hereinbelow. The tripods, trunnions, and inner rollers illustrated anddescribed in this application are intended to be constructed and used inassociation with the constant velocity joints and associated membersthereof as described in the above-identified applicant's priorapplications Ser. No. 11/750,138 (now U.S. Pat. No. 7,819,752) and Ser.No. 11/840,194 (now U.S. Pat. No. 7,878,914), the entire content ofwhich are incorporated herein by reference. Accordingly, detaileddescriptions thereof are not repeated herein for simplicity purposes. Inaddition, it is further noted that the same or similar elements arereferred in the accompanied drawings with the same or similar referencecharacters for simplicity purposes.

FIG. 5 illustrates the tripod for a constant velocity joint according toone preferred embodiment of the present invention, in which FIG. 5( a)shows a partial front view of the tripod, FIG. 5( b) shows across-sectional view of a trunnion of the tripod, taken along thedirections A-A, B-B, and C-C in FIG. 5( a), and FIG. 5( c) shows a sideview of the tripod, seen from the directions D and E in FIG. 5( a).

With reference to FIGS. 5( a)-5(c), the tripod includes three trunnions206 (i.e., 206 i) equally spaced apart around the tripod, in which,however, only one trunnion is shown in the drawing for simplicitypurposes. The trunnion 206 i includes two opposing spherical contactsurfaces (with a spherical diameter OD) disposed in the directionssubject to the load as they are in contact with the inner race of theinner roller, and two opposing flat surfaces in the directionsperpendicular to the spherical contact surfaces and not subject to thecontact load. The trunnion 206 i has a thickness “S” throughout thelength thereof, which is defined by the two parallel and flat surfaces.The space defined between these two opposing flat surfaces and thespherical inner surface of the inner roller is for receiving grease tolubricate the tripod of the invention as is described in the applicant'sprior applications identified above. In this and other embodiments, thethickness “S” is particularly selected to a size the same as or“slightly smaller” than “a maximum non-interfering thickness” (S′) ofthe trunnion.

In this application, the term “maximum non-interfering thickness” (S′)is defined to be a maximum thickness of the trunnion, in which thetrunnion (with two opposing spherical outer contact surfaces of adiameter) is inclined by a predetermined degree (such as degree α inFIGS. 13 and 14) relative to the center axis of the inner roller, andthat can be inserted into the inner roller without interference orwithout applying excessive force. In this application, the term“slightly smaller” or “slightly less than” used in connection with thethickness of the trunnions refers to a size “0-30% smaller” than thereferenced thickness.

A groove 210 of circular or oval shape, recessed from the sphericalsurface of the trunnion, is provided at the central location of eachspherical contact surface of the trunnion 206 as shown in FIGS. 5( b)and 5(c). By the groove 210, the spherical contact surface of thetrunnion is divided into a main spherical contact area 206 a in circular(as shown) or oval shape of predetermined size and a lateral sphericalsurface “J” outside of the central main contact area 206 a. The lateralcontact surface J has the same spherical diameter as that of the centralmain spherical contact surface 206 a, and provides an additional surfacefor contact with the inner surface of the inner roller. Due to thisadditional contact surfaces, the contact surfaces of the trunnion 206provide an enhanced mechanical strength sufficient to endure a potentialhigh stress concentration on the contact surfaces. Alternatively,because the present invention provides more contact surfaces, theoverall size (such as the spherical diameter OD and the thickness S) ofeach trunnion can be reduced than that of the trunnions of theapplicant's prior applications, which receive the contact load only bythe cylindrical protrusions 6 a as illustrated in FIG. 4, whilesatisfying the mechanical strength requirements of the trunnions.

The circular groove 210 recessed from the spherical contact surface ofthe trunnion is for retaining additional grease therein to furtherlubricate the contact surfaces between the trunnions and the generallyspherical inner surface of the inner roller, thus, further enhancing thedurability of the joints under an extended and adverse operationcondition. This lubrication is in addition to the main lubrication to beperformed by the grease retained in the space between the inner surfaceof the inner race and the two opposing planar (or partially curved orangled) surfaces disposed in the directions not subjecting to the load.

FIG. 6 illustrates the tripod for a constant velocity joint according toanother preferred embodiment of the present invention, in which FIG. 6(a) shows a partial front view of the tripod, FIG. 6( b) shows across-sectional view of a trunnion of the tripod, taken along thedirections A-A, B-B, and C-C in FIG. 6( a), and FIG. 6( c) shows a sideview of the tripod, seen from the directions D and E in FIG. 6( a).

With reference to FIGS. 6( a)-(c), this embodiment is similar to theembodiment of FIG. 5 described above, and the detailed descriptions tothe common features thereof are omitted herein and to be referred to thedescription of FIG. 5 above. The main difference of this embodiment overthat of FIG. 5 is that the two opposing side surfaces are shaped to acurved or convex shape having thickness S, which is the maximumnon-interfering thickness to be described later or a thickness slightly(i.e., 0-30%) smaller than the maximum non-interfering thickness, atboth lateral sides of the trunnion for easy assembly, however, havinggreater thickness at the central portions of the trunnion. Due to thisconvex shape, the trunnion of this embodiment has a greater mechanicalstrength than that of FIG. 5, thus enhancing the durability in adverseoperating condition.

FIG. 7 illustrates the tripod for a constant velocity joint according toanother preferred embodiment of the present invention, in which FIG. 7(a) shows a partial front view of the tripod, FIG. 7( b) shows across-sectional view of a trunnion of the tripod, taken along thedirections A-A, B-B, and C-C in FIG. 7( a), and FIG. 7( c) shows a sideview of the tripod, seen from the directions D and E in FIG. 7( a).

With reference to FIGS. 7( a)-(c), this embodiment is similar to theembodiment of FIG. 5 described above, and the detailed descriptions tothe common features thereof are omitted herein and to be referred to thedescription of FIG. 5 above. The main difference of this embodiment overthat of FIG. 5 is that the trunnions do not include the grooves ofcircular or oval shape for retaining additional grease therein tofurther facilitate the lubrication in the contact surface between thetrunnions and the inner rollers. In this embodiment, the lubrication isperformed mainly by the grease retained in the space defined between theinner roller and the side flat surfaces of the trunnions.

FIG. 8 illustrates the tripod for a constant velocity joint according toanother preferred embodiment of the present invention, in which FIG. 8(a) shows a partial front view of the tripod, FIG. 8( b) shows across-sectional view of a trunnion of the tripod, taken along thedirections A-A, B-B, and C-C in FIG. 8( a), and FIG. 8( c) shows a sideview of the tripod, seen from the directions D and E in FIG. 8( a).

With reference to FIGS. 8( a)-(c), this embodiment is similar to theembodiment of FIG. 7 described above, and the detailed descriptions tothe common features thereof are omitted herein and to be referred to thedescription of FIG. 7 above. The main difference of this embodiment overthat of FIG. 7 is that the two opposing side surfaces are shaped into acurved or convex shape having thickness S (which is the maximumnon-interfering thickness or a thickness slightly smaller than themaximum non-interfering thickness) at both lateral sides of the trunnionfor easy assembly, however, having greater thickness at the centralportions of the trunnion. Due to this convex shape, the trunnion of thisembodiment has a greater mechanical strength than that of FIG. 7, thusenhancing the durability in adverse operating condition.

With reference to FIG. 14, described below are the underlying reasonsfor particularly selecting the thickness of the trunnion to include thethickness S throughout the trunnion (as in FIGS. 5 and 7) or at leastone lateral side of the trunnion (as in FIGS. 6, 8, 9-10) for assemblyand other considerations.

To assemble the trunnion into the inner roller 204, the roller assembly,having inner roller 204 installed within outer roller 203 with needlerollers retained therein, is tilted to assume an inclined angle a withrespect to the trunnion, as illustrated in FIGS. 13 and 14. Wheninclined, the spherical outer surface of the trunnion 206, composed ofthe center contact area 206 a and the lateral spherical area J, projectsinto an elliptical shape when viewed from the angle of the inner roller204. As shown in FIG. 14, if the trunnion has a thickness T, which islarger than the maximum non-interfering thickness S′, theelliptically-projected surface includes hatched areas W at four cornersof the trunnion, where the inner roller 204 collides and interferes withthe elliptical shaped trunnion for assembly.

However, if the trunnion has a thickness S′ (the maximum non-interferingthickness), as shown in FIGS. 5-8 and 13, or a thickness slightlysmaller than S′, the inner roller 204 does not interfere with theelliptically projected outer surface of the trunnion for assembly. Forthis reason, it is crucial to have the thickness S′ or smaller size atone or both lateral sides of the trunnion.

As such, the thickness of trunnion is typically to be reduced from “T”to “S” (as shown in FIG. 5) in order to assemble the trunnion into theinner roller without interference. However, when the entire thickness ofthe trunnion is reduced to the thickness S, the cross-sectionaldimension of the neck of the trunnion (defined between the trunnion andthe shoulder there-below) is also to be reduced to meet the designrequirements and assembly considerations of the tripod. As a result,when the dimension of the neck portion is reduced, the trunnion may havean insufficient bending strength particularly around the neck of thetrunnion. Accordingly, one solution to this strength deteriorationproblem in the neck portion is to have the trunnion into a convexcross-sectional shape of enhanced dimension as shown in FIGS. 6 and 8.When having the convex-shaped trunnion, the neck portion of the trunnioncan be enlarged and the mechanical strength in the neck of the trunnioncan be enhanced.

Moreover, as detailed below, the applicant of this invention furtherrecognized another potential drawback in the embodiments of theinvention described above in connection with FIGS. 5-8, which have thethickness S at both lateral sides of the trunnion to contact the innersurface of the inner roller. That is, by having the smaller thickness Sat both lateral sides of the trunnion 206 (e.g., 206 i, 206 j, 206 k,and 206 l shown in FIGS. 5-8), the spherical contact surface between theinner roller and the trunnion is also reduced. As a result, the maximumload to be supported by the trunnion and the inner roller is limited,and thus, weakening the durability of the system. Accordingly, withreference to FIGS. 9-11, the applicant further provides the followingsolutions to this and above described drawbacks, while also satisfyingthe assembly considerations of the tripod system.

With reference to FIGS. 9-11, the trunnion 206 m has a complex shapewith its cross-sectional dimension gradually varying between T and S,preferably in an alternating manner, relative to the axial coordinatedistance from the neck or center of the trunnion, while satisfying theassembly consideration discussed above and further enhancing themechanical strength and durability of the trunnion.

More particularly, in order to secure more contact surface to thetrunnion 206 and also to provide a sufficient bending strength to theneck portion 207, the cross-sectional shape taken at the upper portionof the trunnion has a larger thickness “T” at one side (e.g., the leftside) and is gradually decreased until it reaches a smaller thickness“S” at the opposite side (e.g., the right side) of the trunnion, asshown in FIG. 10( b). To the contrary, the cross-sectional shape takenat the lower portion of the trunnion has an opposing or generallysymmetrical shape with a smaller thickness “S” at the left side and thethickness is gradually increased until it reaches a larger thickness “T”at the right side of the trunnion, as shown in FIG. 10( d). Thecross-sectional shapes in-between the upper and lower portions aregradually and continuously varied from the cross-sectional shape at theupper portion to the cross-sectional shape at the lower portion of thetrunnion. As a result, the cross-sectional shape taken at the middleportion of the trunnion includes a generally planar shape or a slightlyconvex shape, as shown in FIG. 10( c), with the side thickness “L”having a dimension between “T” and “5”.

The dimensions of S and T can be determined in the range defined by thefollowing equations:

0.5 D≦S≦0.7 D;

1.0 S≦T≦1.2 S;

wherein D is the spherical diameter of the trunnion.

Referring still to FIGS. 9-11, this embodiment includes members andfeatures common with that of the embodiments shown in FIGS. 5 and 6described above. The detailed descriptions of such common features (forexample, such as groove 210, main spherical contact area 206 a, andlateral spherical contact area J) are omitted herein and to be referredto the description of FIG. 5 above.

wow Preferred assembly methods of the constant velocity joint of thepresent invention are described herein below in connection with only theembodiment of FIGS. 9-11. Assembly methods for other embodiments of theinvention before described would be based on similar concepts andmethods described herein. Accordingly, those skilled in the art willappreciate or recognize that various modifications and substitutions canbe made thereto without departing from the spirit, concepts, and aspectsof the assembly methods described below.

With reference to FIG. 12( a), the roller assembly having the innerroller 204 received in the outer roller 203 is tilted to assume aninclination degree α relative to the axis of the trunnion 206. Then, onelower side (e.g., the lower right side) of the inner roller 204 of theroller assembly is placed on one upper side (e.g., the upper right side206 b) of the trunnion, and the other lower side (e.g., the lower leftside) of the inner roller 204 is positioned into the trunnion 206 tomeet the corresponding lower side (e.g., the lower left side 206 c) ofthe trunnion as shown. By this arrangement, because both the upper rightside 206 b and the lower left side 206 c of the trunnion have sphericalcontact surfaces with the smaller thickness S as shown in FIG. 12( c)and FIG. 12( b), respectively, the inner roller 204 can be easilyassembled onto the trunnion 206 by suitably rotating the inner roller204 about the spherical contact surface of the trunnion with the lowerleft side 206 c of the trunnion using as a pivot center for the innerroller 204. This assembly can be performed without any interferencebetween the parts or without applying excessive external force forassembly. This assembly method of the invention is illustrated in FIG.13. To the contrary, FIG. 14 illustrates an opposite example in whichthe trunnion has the larger thickness T at both corresponding assemblysides thereof, and interferes with the inner roller 204 by the hatchedregions W.

With reference to FIGS. 15( a)-(c), another preferred embodiment of thepresent invention is described herein. In this embodiment, in order tosecure more contact surface to the trunnion 206 n and also to provide asufficient bending strength to the neck portion 207, the cross sectionalshape of the trunnion has a complex shape with its thickness in crosssection preferably varying relative to the axial coordinate distancefrom the neck or center of the trunnion in an alternating manner. Inthis embodiment, the cross-sectional shape taken at the upper portion ofthe trunnion has the larger thickness “T” at one side (e.g., the leftside) and the smaller thickness “S” at the opposite side (e.g., theright side) of the trunnion, and the cross-sectional contour between theleft and right sides is gradually varied to define a convex shape as awhole, preferably with the contour thereof defined by a surface radiusR, as shown in FIG. 15( b). To the contrary, the cross-sectional shapetaken at the lower portion of the trunnion has the smaller thickness “S”at the left side and the larger thickness “T” at the right side, and thecross-sectional contour between the left and right sides is graduallyvaried to define a convex shape as a whole, preferably with the contourthereof defined by a surface radius R, as shown in FIG. 15( c). Thecross-sectional shapes in-between the upper and lower portions aregradually varied from the cross-sectional shape at the upper portion tothe cross-sectional shape at the lower portion of the trunnion. As aresult, the cross-sectional shape taken at the middle portion of thetrunnion (not shown) includes a generally planar shape or a slightlyconvex shape, with the two lateral side thicknesss having a dimensionbetween “T” and “S”. Other aspects of this embodiment (including theassembly methods thereof) are similar to that of the previous embodimentof FIGS. 9-11, and the detailed descriptions to such common aspects areomitted herein and to be referred to the description of FIGS. 9-11above.

In this embodiment, the dimensions of S, T, and R can be determined inthe range defined by the following equations:

0.5 D≦S≦0.7 D;

1.0 S≦T≦1.2 S;

0.8 D≦R≦1.5 D;

wherein D is the spherical diameter of the trunnion, and R is the radiusof the side surfaces of the trunnion appeared in the cross sections atthe upper and lower portions the trunnion .

With reference to FIG. 16, another preferred embodiment of the presentinvention is described herein. This embodiment is similar to theembodiment of FIG. 6 described above, and the detailed descriptions tothe common features thereof are omitted herein and to be referred to thedescription of FIG. 6 above. The main difference of this embodiment overthat of FIG. 6 is that the two opposing side surfaces are shaped to anangled shape (instead of a curved or convex shape) and having thethickness S at both lateral sides of the trunnion for easy assembly,however, having an enlarged angled portion in-between the two lateralsides with chamfer Ω defined by the angled surface, as shown in thedrawing. Due to the enlarged portion, the trunnion of this embodimenthas a greater mechanical strength than that of FIG. 5, and thus,enhancing the durability of the trunnion.

With reference to FIG. 17, another preferred embodiment of the presentinvention is described herein. This embodiment is similar to theembodiment of FIG. 16 described above, and the detailed descriptions tothe common features thereof are omitted herein and to be referred to thedescription of FIG. 16 above. The main difference of this embodimentover that of FIG. 16 is that the center of the trunnion neck 206 d isoffset from the center (Y-Y) of the trunnion 206 by a distance of Δ, asshown in FIG. 17. Having the offset neck 206 d, the assembly of thetrunnion 206 into the inner roller is further facilitated. For assembly,the roller assembly (having the inner roller 204 received in the outerroller 204 with needle bearings there-between) is first tilted to assumean inclination degree α relative to the axis of the trunnion 206. Then,one lower side (e.g., the lower right side) of the inner roller 204 ofthe roller assembly is placed on one upper side (e.g., the upper rightside 206 b) of the trunnion, and the other lower side (e.g., the lowerleft side) of the inner roller 204 is positioned into the trunnion 206to meet the corresponding lower side (e.g., the lower left side 206 c)of the trunnion, where the thinner neck portion 206 d is present by theoffset of the neck, as illustrated in FIG. 18( d). By this arrangement,because both the upper right side 206 b and the lower left side 206 c ofthe trunnion, respectively, have the smaller thickness S (as shown inFIG. 17) and also due to the smaller neck portion 206 d, the innerroller 204 can be easily assembled onto the trunnion 206 by suitablyrotating the inner roller 204 about the spherical contact surface of thetrunnion with the lower left side 206 c of the trunnion using as a pivotcenter for the inner roller 204. This assembly can be performed withoutany interference between the parts and without applying excessiveexternal force for assembly.

With reference to FIG. 18, another preferred embodiment of the presentinvention is described herein. As is similar to the embodiment of FIG.17 described above, in this embodiment the center of the trunnion neck206 d is also offset from the center (Y-Y) of the trunnion 206 by adistance of Δ, as shown in FIG. 18( a). The main difference of thisembodiment over that of FIG. 17 is that the thickness of the trunnion atone lateral side, in a direction of receiving the load, is “T”, and theinner roller 204 further includes two small grooves 204 b or one largegroove 204 b at the lower inner surface thereof, as respectively shownin FIGS. 18( b) and 18(c).

In this embodiment, although the trunnion has a larger thickness T atone lateral side subjecting to the load, the assembly can be easily doneutilizing the offset neck 206 d along with the lower grooves 204 b ofthe inner roller. For assembly, the roller assembly having the innerroller 204 received in the outer roller 204 is first tilted to assume aninclination degree α relative to the axis of the trunnion 206. Then, onelower side face (e.g., the lower right side) of the inner roller 204 ofthe roller assembly is placed on one upper side (e.g., the upper rightside 206 b) of the trunnion, and the other lower side (e.g., the lowerleft side) of the inner roller 204 is positioned into the trunnion 206to meet the corresponding lower side (e.g., the lower left side 206 c)of the trunnion, where the smaller neck portion 206 d is present by theneck offset, as illustrated in FIG. 18( d). Here, the potentialinterference by the larger thickness T of the trunnion, is assumed bythe grooves 204 b, namely, by placing the upper right edges of thetrunnion in the grooves 204 b of the inner roller as shown in thedrawing. Thereafter, the remaining assembly processes are completed in asimilar manner described above, without any interference between theparts and without applying excessive external force for assembly.

As described above in association with various exemplary embodimentsthereof, the present invention provides a constant velocity joint havinga reliable and durable structure, easy to assemble, and with sufficientmechanical strength suitable for using as torque transfer joints in thedrive axle of an automobile, for example.

The above disclosed embodiments of the invention are representatives ofa presently preferred form of the invention, but are intended to beillustrative rather than definitive thereof. Accordingly, those skilledin the art will appreciate or recognize that various modifications andsubstitutions can be made thereto without departing from the spirit andscope of the present invention as set forth in the appended claims.

1. A method of assembling a trunnion of a constant velocity joint intoan inner roller of a roller assembly, comprising: providing a rollerassembly for a constant velocity joint, the roller assembly including anouter roller, and an inner roller having a spherical inner face;providing a constant velocity joint having a tripod with a pluralitytrunnions, each trunnion including two opposing spherical contactsurfaces disposed in the directions subject to the load, and twoopposing side surfaces disposed between the two opposing sphericalcontact surfaces and in the directions not subject to the load;measuring a maximum non-interfering thickness of the trunnion which is amaximum thickness of the trunnion, having the two opposing sphericalcontact surfaces of a diameter, that can be inserted into the innerroller without interference while inclining the inner roller by apredetermined degree relative to the longitudinal axis of the trunnion;providing the trunnion to have a cross sectional shape, the crosssection taken in a direction perpendicular to the longitudinal axis ofthe trunnion, with a first thickness at one lateral side of the trunnionand a second thickness at the other lateral side of the trunnion, whereone or both of the first and second thicknesses have a size the same asor 0-30% smaller than the maximum non-interfering thickness of thetrunnion; inclining the inner roller with respect to the trunnion toassume the predetermined degree of inclination; positioning the inclinedinner roller partially onto the trunnion, by placing a lower right innerface of the inner roller on an upper right side of the trunnion andpositioning a lower left inner face of the inner roller to meet a lowerleft side of the trunnion; and completely positioning the inner rollerby pushing or rotating a right upper side of the inclined inner rollerdown without applying excessive external force.
 2. The method of claim1, wherein the trunnion is provided to have a neck portion below thetrunnion, with the center line of neck portion generally coaxial withthe longitudinal axis of the trunnion.
 3. The method of claim 1, whereinthe trunnion is provided to have a neck portion below the trunnion, withthe center line of neck portion offset from the longitudinal axis of thetrunnion, and said positioning the lower left face of the inner rolleris performed to meet the lower left side of the trunnion where the neckportion has a smaller thickness by the offset.
 4. The method of claim 1,wherein the inner roller is provided with one or two grooves formed at alower inner face of the inner roller, and said placing the lower rightinner face of the inner roller on an upper right side of the trunnion isperformed by placing the upper right side of the trunnion in the one ortwo grooves of the inner roller.
 5. The method of claim 1, wherein thetrunnion is provided to have a cross sectional shape, throughout theentire cross sections taken in the direction perpendicular to thelongitudinal axis of the trunnion, with both the first thickness at theone lateral side and the second thickness at the other lateral side inthe same size which is the same as or 0-30% smaller than the maximumnon-interfering thickness of the trunnion.
 6. The method of claim 1,wherein the trunnion is provided to have a cross sectional shape,throughout the entire cross sections taken in the directionperpendicular to the longitudinal axis of the trunnion, with the firstthickness at the one lateral side being larger than the second thicknessat the other lateral side, and the first and second thicknesses aredefined by the equations of:S=(0.5−0.7)×D;T=(1.0−1.2)×S; where S represents the second thickness at the otherlateral side of the trunnion which is the same as or 0-30% smaller thanthe maximum non-interfering thickness, T represents the first thicknessat the one lateral side of the trunnion which is larger than the maximumnon-interfering thickness of the trunnion, and D represents a sphericaldiameter of the trunnion.
 7. The method of claim 6, wherein the trunnionis provided to have a cross sectional shape with the thickness generallydecreasing from the first thickness at the first lateral side to thesecond thickness at the second lateral side of the trunnion.
 8. Themethod of claim 1, wherein the trunnion is provided to have a crosssectional shape, taken in the direction perpendicular to thelongitudinal axis of the trunnion, with the first thickness at the onelateral side being larger than the second thickness at the other lateralside, and the first and second thicknesses are defined by the equationsof:S=(0.5−0.7)×D;T=(1.0−1.2)×S; where S represents the second thickness at the otherlateral side of the trunnion which is the same as or 0-30% smaller thanthe maximum non-interfering thickness, T represents the first thicknessat the one lateral side of the trunnion which is larger than the maximumnon-interfering thickness of the trunnion, and D represents a sphericaldiameter of the trunnion; and wherein the cross sectional shape of thetrunnion varies with the thickness gradually varying from the firstlateral side of the trunnion to the second lateral side of the trunnionin an alternate manner relative to an axial distance from the center ofthe tripod, and in a manner such that, by said placing the lower rightinner face of the inner roller on the upper right side of the trunnionand by said positioning the lower left inner face of the inner roller tomeet the lower left side of the trunnion, the inclined inner roller ispartially positioned onto the trunnion with its spherical inner facepartially receiving the upper right side of the trunnion with thethickness S and partially receiving the lower left side of the trunnionwith the thickness S.
 9. The method of claim 8, wherein the trunnion isprovided to have a neck portion below the trunnion, with the center lineof neck portion generally coaxial with the longitudinal axis of thetrunnion.
 10. The method of claim 8, wherein the trunnion is provided tohave a neck portion below the trunnion, with the center line of neckportion offset from the longitudinal axis of the trunnion, and saidpositioning the lower left face of the inner roller is performed to meetthe lower left side of the trunnion where the neck portion has a smallerthickness by the offset.
 11. The method of claim 10, wherein the innerroller is provided with one or two grooves formed at a lower inner faceof the inner roller, and said placing the lower right inner face of theinner roller on an upper right side of the trunnion is performed byplacing the upper right side of the trunnion in the one or two groovesof the inner roller.